1988 OMC 5.7 Overheating Problem

[tom Carlson]

I have a 88 Four Winns Vista 245 with a 5.7 OMC engine. The engine recently started to overheat. I immediately changed the outdrive pump but the problem continued. The temp gauge was not registering leading me to believe water was not getting to the temp sensor located on the intake manifold. To be on the safe side I replaced the thermostat, the temp gauge started to work and the engine warmed to 160 degrees and worked fine for a 45 minute test run. One week later the engine started to overheat and the gauge did not register. I pulled each cooling hose with the engine running and have a strong head of water from the outdrive, flow of water to the exhaust manifold (possibly from the thermostat bypass?). I checked the circulation pump no leaks or slack on the shaft. When I opened the petcock on the bottom end of the engine water flowed out. The boat is used in Lake Michigan so corrosion should not be a big issue. Could this be a circulation pump problem? If so how would I test that pump? Does the outdrive pump have enough power to pump water past the circulation pump and get water into the upper engine and intake manifold cooling passages? Before I tear anything else apart does anyone have ideas on what to look at next?

 

[Gary H NC]

Re: 1988 OMC 5.7 Overheating Problem

Welcome to Iboats Tom,

Was any of the old impeller missing? If so it could be a blockage somewhere.
Usually where the water inlet hose goes through the power steering cooler.
Clean the connections and tighten the wire to the temp sender too...

 

[tom Carlson]

Re: 1988 OMC 5.7 Overheating Problem

I checked the flow through the cooler and the flow is 2" to 3". The flow to the exhaust manifold seems a little low like it is being pumped through the thermostat bypass. I guess my next step might be to pull the circulation pump to see if the blades are damages of if there is blockage at that point and to recheck the thermostat to make sure it is not defective. It would be my luck to get a new thermostat that is DOA.

Oh well what is summer boating for, using the boat for a few hours and then spending hours and hours trouble shooting. It is amazing that the guys who service the boat seem to be at a loss. They are certified which makes me nervous about having them touch anything other than oil changes.